Maintenance liquid and maintenance method

ABSTRACT

There is provided a maintenance liquid, which is used in maintenance of a device equipped with a discharge head for discharging an ultraviolet ray curable-type composition containing the acyl phosphine oxide-based photopolymerization initiator toward an attachment object, including a polymerizable compound in which a saturation solubility of an acyl phosphine oxide-based photopolymerization initiator at 20° C. is equal to or greater than 5.0% by mass.

BACKGROUND

1. Technical Field

The present invention relates to a maintenance liquid and a maintenancemethod.

2. Related Art

In the ink jet recording method, a high-resolution image can be recordedwith a relatively simple device, and rapid development has been achievedin various fields. For example, in JP-A-2012-31389, for the purpose ofproviding a method of reducing defects in a pattern transfer even in thecase of performing transfer of an ultra fine pattern, a maintenanceliquid which is used in an ink jet device using a pattern forming methodincluding discharging a photocurable composition which has apolymerizable monomer as a main component on a substrate or a moldhaving a fine pattern using an ink jet device and irradiating thephotocurable composition with light in the state of being sandwichedbetween the substrate and the mold having a fine pattern, and contains acompound having an ester and/or ether functional group is disclosed.

However, in the maintenance liquids in the related art described inJP-A-2012-31389, there is a problem that the polymerization initiator inthe ultraviolet ray curable-type composition (photocurable composition)is precipitated at the time of maintenance, and due to this, cleaningability is reduced. In particular, in the case where a large amount ofthe polymerization initiator is included in the ultraviolet raycurable-type composition in order to ensure curability, this problembecomes significant.

SUMMARY

An advantage of some aspects of the invention is to provide amaintenance liquid which has a high cleaning ability at the time ofmaintenance, can suppress reduction in the curability of the ultravioletray curable-type composition after maintenance, and can be used inmaintenance of the ultraviolet ray curable-type composition having anexcellent curability of the ultraviolet ray curable-type composition.

The present inventors repeated thorough studies. As a result, theinvention is realized by using a predetermined polymerizable compound.

That is, the invention is as follows.

[1] According to an aspect of the invention, there is provided amaintenance liquid which includes a polymerizable compound in which asaturation solubility of an acyl phosphine oxide-basedphotopolymerization initiator at 20° C. is equal to or greater than 5.0%by mass, and which is used in maintenance of a device equipped with adischarge head for discharging an ultraviolet ray curable-typecomposition containing the acyl phosphine oxide-basedphotopolymerization initiator toward an attachment object.

[2] In the maintenance liquid according to [1], the polymerizablecompound may include at least any one of vinyl ether group-containing(meth)acrylic acid ester represented by the following general formula(1) and a monofunctional (meth)acrylate compound having an aromaticring.

CH₂═CR¹—COOR²—O—CH═CH—R³  (1)

(In the formula (1), R² represents a hydrogen atom or a methyl group, R²represents a divalent organic residue having 2 to 20 carbon atoms, andR³ represents a hydrogen atom or a monovalent organic residue having 1to 11 carbon atoms.)

[3] In the maintenance liquid according to [1] or [2], the viscosity ofthe polymerizable compound at 20° C. may be equal to or less than 30mPa·s.

[4] In the maintenance liquid according to any one of [1] to [3], thecontent of the polymerizable compound may be equal to or greater than40% by mass with respect to the total amount of the maintenance liquid.

[5] In the maintenance liquid according to any one of [1] to [4], theviscosity at 20° C. may be equal to or less than 20 mPa·s.

[6] In the maintenance liquid according to any one of [1] to [5], theviscosity at 20° C. may be lower than the viscosity of the ultravioletray curable-type composition at 20° C. by equal to or greater than 5mPa·s.

[7] In the maintenance liquid according to any one of [1] to [6], theultraviolet ray curable-type composition may include the polymerizablecompound, and the content of the polymerizable compound in themaintenance liquid is larger than the content of the polymerizablecompound in the ultraviolet ray curable-type composition by equal to orgreater than 10% by mass.

[8] In the maintenance liquid according to any one of [1] to [7], thesaturation solubility of the acyl phosphine oxide-basedphotopolymerization initiator at 20° C. with respect to thepolymerizable compound may be equal to or greater than 8.0% by mass.

[9] The maintenance liquid according to any one of [1] to [8] mayfurther include at least any one of a silicone-based surfactant and afluorine-based surfactant.

[10] In the maintenance liquid according to any one of [1] to [9], themolecular weight of the polymerizable compound may be equal to orgreater than 170.

[11] In the maintenance liquid according to any one of [1] to [10], thecontent of the acyl phosphine oxide-based photopolymerization initiatorin the ultraviolet ray curable-type composition may be equal to orgreater than 5.0% by mass.

[12] In the maintenance liquid according to any one of [1] to [11], asolubility parameter may be equal to or greater than 5.0.

[13] In the maintenance liquid according to any one of [1] to [12], thesaturation solubility may be a saturation solubility ofbis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide at 20° C.

[14] According to another aspect of the invention, there is provided amaintenance method including performing maintenance of a device equippedwith a discharge head for discharging an ultraviolet ray curable-typecomposition containing an acyl phosphine oxide-based photopolymerizationinitiator toward an attachment object using the maintenance liquidaccording to any one of [1] to [13].

[15] In the maintenance method according to [14], the device may beequipped with an ultraviolet ray emitting diode for irradiating thedischarged ultraviolet ray curable-type composition with ultravioletrays, and the ultraviolet ray emitting element may have an emission peakwavelength in a range of 360 nm to 420 nm.

[16] In the maintenance method according to [14] or [15], the device maybe equipped with a heating mechanism for heating the ultraviolet raycurable-type composition, and may discharge the heated composition.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, aspects for carrying out the invention (hereinafter,referred to as “the embodiment”) will be described in detail. Further,the invention is not limited thereto, and various modifications arepossible without departing from the gist of the invention.

Maintenance Liquid

The maintenance liquid of the embodiment includes a polymerizablecompound in which a saturation solubility of an acyl phosphineoxide-based photopolymerization initiator at 20° C. is equal to orgreater than 5.0% by mass, and is used in maintenance of a deviceequipped with a discharge head for discharging an ultraviolet raycurable-type composition containing the acyl phosphine oxide-basedphotopolymerization initiator to an attachment object.

Polymerizable Compound

The maintenance liquid of the embodiment includes a polymerizablecompound in which a saturation solubility of an acyl phosphineoxide-based photopolymerization initiator at 20° C. is equal to orgreater than 5.0% by mass. By including such a polymerizable compound,cleaning ability at the time of maintenance is further improved, andreduction in the curability of an ultraviolet ray curable-typecomposition after maintenance can be further suppressed.

In addition, the saturation solubility of the acyl phosphine oxide-basedphotopolymerization initiator in the polymerizable compound at 20° C. isequal to or greater than 5.0% by mass, preferably equal to or greaterthan 8.0% by mass, and more preferably equal to or greater than 10% bymass. The polymerizable compound, in which the saturation solubility isequal to or greater than 5.0% by mass, tends to further improve cleaningability at the time of maintenance. Moreover, the upper limit of thesaturation solubility of the acyl phosphine oxide-basedphotopolymerization initiator in the polymerizable compound at 20° C. isnot particularly limited, however, the upper limit is preferably equalto or less than 20% by mass.

The content of the polymerizable compound is preferably equal to orgreater than 40% by mass, more preferably equal to or greater than 50%by mass, still more preferably equal to or greater than 65% by mass withrespect to the total amount of the maintenance liquid. When the contentof the polymerizable compound is equal to or greater than 40% by mass,there is a tendency that cleaning ability at the time of maintenance isfurther improved, and reduction in the curability of the ultraviolet raycurable-type composition after maintenance is further suppressed. Inaddition, the content of the polymerizable compound is preferably equalto or less than 90% by mass, more preferably equal to or less than 85%by mass, and still more preferably equal to or less than 80% by masswith respect to the total amount of the maintenance liquid. When thecontent of the polymerizable compound is equal to or less than 90% bymass, flexibility of design of the maintenance liquid is increased, andthus, balance with other characteristics such as reduction in viscosityof the maintenance liquid becomes excellent in some cases.

In particular, the content of the polymerizable compound in which thesaturation solubility of the acyl phosphine oxide-basedphotopolymerization initiator at 20° C. is equal to or greater than 8.0%by mass is preferably 30% by mass to 80% by mass, and more preferably40% by mass to 80% by mass, still more preferably 50% by mass to 80% bymass. When the content of the polymerizable compound in which thesaturation solubility of the acyl phosphine oxide-basedphotopolymerization initiator at 20° C. is equal to or greater than 8.0%by mass is in the above range, there is a tendency that cleaning abilityat the time of maintenance is further improved, and reduction in thecurability of the ultraviolet ray curable-type composition aftermaintenance is further suppressed.

The saturation solubility of the acyl phosphine oxide-basedphotopolymerization initiator at 20° C. can be obtained by a method formeasuring a saturation solubility in Examples described below. Moreover,the acyl phosphine oxide-based photopolymerization initiators at thetime of determining the saturation solubility of the acyl phosphineoxide-based photopolymerization initiator in the polymerizable compoundat 20° C. are the same as those used in the measurement of thesaturation solubility in Examples described below.

The polymerizable compound is not particularly limited, and for example,monofunctional, bifunctional, and tri- or higher functional monomers andoligomers known in the related art can be used. The polymerizablecompounds may be used alone or two or more kinds may be used incombination. Among these, the polymerizable compound preferably includesat least any one of vinyl ether group-containing (meth)acrylic acidester represented by the following general formula (1) and amonofunctional (meth)acrylate compound having an aromatic ring. Thepolymerizable compounds may be used alone or two or more kinds may beused in combination.

CH₂═CR¹—COOR²—O—CH═CH—R³  (1)

(In the above formula (1), R¹ represents a hydrogen atom or a methylgroup, R² represents a divalent organic residue having 2 to 20 carbonatoms, and R³ represents a hydrogen atom or a monovalent organic residuehaving 1 to 11 carbon atoms.)

Vinyl Ether Group-Containing (Meth)acrylic Acid Ester

When the maintenance liquid contains vinyl ether group-containing(meth)acrylic acid ester represented by the general formula (1), thereis a tendency that cleaning ability at the time of maintenance isfurther improved, and reduction in the curability of the ultraviolet raycurable-type composition after maintenance is further suppressed.

Examples of the divalent organic residue having 2 to 20 carbon atomsrepresented by R² in the general formula (1) include a linear, branched,or cyclic alkylene group having 2 to 20 carbon atoms, which may havebeen substituted, an alkylene group having 2 to 20 carbon atoms, whichmay have been substituted, having an oxygen atom by an ether bond and/oran ester group in the structure, and a divalent aromatic group having 6to 11 carbon atoms, which may have been substituted. Among these, analkylene group having 2 to 6 carbon atoms such as an ethylene group, ann-propylene group, an isopropylene group, or a butylene group, and analkylene group having 2 to 9 carbon atoms having an oxygen atom by anether bond in the structure, such as an oxyethylene group, anoxy-n-propylene group, an oxyiso propylene group, or an oxybutylenegroup are suitably used.

As the monovalent organic residue having 1 to 11 carbon atomsrepresented by R³ in the general formula (1), a linear, branched, orcyclic alkyl group having 1 to 11 carbon atoms, which may have beensubstituted, and a monovalent aromatic group having 6 to 11 carbonatoms, which may have been substituted, are suitable. Among these, analkyl group having 1 or 2 carbon atoms, which is a methyl group or anethyl group and a monovalent aromatic group having 6 to 8 carbon atomssuch as a phenyl group or a benzyl group are suitably used.

In a case where each organic residue described above is a group whichmay have been substituted, the substituent is divided into a group whichhas a carbon atom and a group which does not have a carbon atom. First,in a case where the above substituent is a group having a carbon atom,the number of the carbon atom is counted in the number of carbon atomsin the organic residue. Next, examples of the group having a carbonatom, which are not particularly limited, include a carboxyl group andan alkoxy group. Next, examples of the group not having a carbon atom,which are not particularly limited, include a hydroxyl group and a halogroup.

Examples of the vinyl ether group-containing (meth)acrylic acid ester,which are not particularly limited, include 2-(2-vinyloxyethoxyl)ethylacrylate.

The content of the vinyl ether group-containing (meth)acrylic acid esteris preferably 15% by mass to 55% by mass, more preferably 20% by mass to50% by mass, still more preferably 25% by mass to 45% by mass withrespect to the total amount of the maintenance liquid. When the contentof the vinyl ether group-containing (meth)acrylic acid ester is equal toor greater than 15% by mass, curability tends to be further improved. Onthe other hand, when the content of the vinyl ether group-containing(meth)acrylic acid ester is equal to or less than 55% by mass,preservation stability tends to be further improved.

Monofunctional (Meth)Acrylate Compound Having Aromatic Ring

Examples of the monofunctional (meth)acrylate compound having anaromatic ring, which are not particularly limited, include phenoxyethylacrylate, 2-hydroxy-3-phenoxypropyl acrylate, and benzyl acrylate. Themonofunctional (meth)acrylate compound having an aromatic ring may beused alone or two or more kinds may be used in combination.

The content of the monofunctional (meth)acrylate compound having anaromatic ring is preferably 5.0% by mass to 90% by mass, more preferably10% by mass to 85% by mass, still more preferably 15% by mass to 80% bymass with respect to the total amount of the maintenance liquid. Whenthe content of the monofunctional (meth)acrylate compound having anaromatic ring is equal to or greater than 5.0% by mass, curability tendsto be further improved. On the other hand, when the content of themonofunctional (meth)acrylate compound having an aromatic ring is equalto or less than 90% by mass, friction resistance tends to be furtherimproved.

The molecular weight of the polymerizable compound included in themaintenance liquid is preferably equal to or greater than 170, morepreferably equal to or greater than 190, and still more preferably equalto or greater than 210. When the molecular weight of the polymerizablecompound is equal to or greater than 170, odor tends to be less likelyto occur. In addition, although the upper limit of the molecular weightof the polymerizable compound is not particularly limited, the upperlimit is preferably equal to or less than 300.

The viscosity of the polymerizable compound included in the maintenanceliquid at 20° C. is preferably equal to or less than 30 mPa·s, morepreferably equal to or less than 20 mPa·s, and still more preferablyequal to or less than 15 mPa·s. When the viscosity of the polymerizablecompound included in the maintenance liquid at 20° C. is equal to orless than 30 mPa·s, cleaning ability tends to be further improved.Although the lower limit of the viscosity of the polymerizable compoundat 20° C. is not particularly limited, the lower limit is preferablyequal to or greater than 1 mPa·s. Moreover, in a case where themaintenance liquid includes plural polymerizable compounds as a mixture,the viscosity described here refers to the viscosity of the mixture.

Moreover, the maintenance liquid may further include a polymerizablecompound in which the saturation solubility of the acyl phosphineoxide-based photopolymerization initiator at 20° C. is less than 5.0% bymass. Examples of the polymerizable compound, which are not particularlylimited, include dipropylene glycol diacrylate, isobornyl acrylate,dipentaerythritol hexaacrylate, isooctyl acrylate, and lauryl acrylate.

Surfactant

The maintenance liquid of the embodiment may include a surfactant.Examples of the surfactant, which are not particularly limited, includea silicone-based surfactant, a fluorine-based surfactant, and anacetylene glycol surfactant. Among these, the surfactant in theembodiment preferably includes at least any one of the silicone-basedsurfactant and the fluorine-based surfactant.

Examples of the silicone-based surfactant include a polysiloxane-basedcompound and polyether-modified organosiloxane. Specific examples ofcommercially available products of the silicone-based surfactants, whichare not particularly limited, include BYK-306, BYK-307, BYK-333,BYK-341, BYK-345, BYK-346, BYK-347, BYK-348, BYK-349, and BYK-UV3500(hereinbefore, all are trade names, manufactured by BYK Japan KK), andKF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640,KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, andKF-6017 (hereinbefore, all are trade names, manufactured by Shin-EtsuChemicals Co., Ltd.).

Examples of the fluorine-based surfactant, which are not particularlylimited, include a perfluoroalkyl sulfonate, a perfluoroalkylcarboxylate, a perfluoroalkyl phosphoric acid ester, a perfluoroalkylethylene oxide adduct, a perfluoroalkyl betaine, and a perfluoroalkylamine oxide compound. Examples of commercially available products of thefluorine-based surfactant, which are not particularly limited, includeS-144 and S-145 (manufactured by Asahi Glass Co., Ltd.); FC-170C,FC-430, and Fluorad-FC4430 (manufactured by Sumitomo 3M Ltd.); FSO,FSO-100, FSN, FSN-100, and FS-300 (manufactured by Dupont); and FT-250,and 251 (manufactured by Neos Company Limited). The fluorine-basedsurfactants may be used alone or two or more kinds may be used incombination.

The acetylene glycol-based surfactant are not particularly limited, andfor example, one or more kinds selected from an alkylene oxide adduct of2,4,7,9-tetramethyl-5-decyne-4,7-diol and2,4,7,9-tetramethyl-5-decyne-4,7-diol, and an alkylene oxide adduct of2,4-dimethyl-5-decyn-4-ol and 2,4-dimethyl-5-decyn-4-ol are preferable.Examples of commercially available products of the acetyleneglycol-based surfactant, which are not particularly limited, includeOlfine 104 series, and E series (trade name, manufactured by AirProducts Japan, Inc.) such as Olfine E1010, and Surfynol 465 andSurfynol 61 (trade name, manufactured by Nissin Chemical Industry Co.,Ltd.). The acetylene glycol-based surfactants may be used alone or twoor more kinds may be used in combination.

The content of the surfactant is preferably 0.1% by mass to 5% by mass,and more preferably 0.1% by mass to 3% by mass with respect to the totalamount of the maintenance liquid. When the content of the surfactant isin the above range, there is a tendency that wettability of themaintenance liquid with respect to the portion contacting themaintenance liquid of a recording apparatus is further improved, andcleaning ability is further improved.

Polymerization Inhibitor

The maintenance liquid of the embodiment may include a polymerizationinhibitor. Examples of the polymerization inhibitor, which are notparticularly limited, include hydroquinones such as hydroquinone,hydroquinone monomethyl ether (MEHQ), 1-o-2,3,5-trimethyl hydroquinone,and 2-tert-butylhydroquinone; catechols such as catechol, 4-methylcatechol, and 4-tert-butylcatechol; phenols such as phenol, butylhydroxytoluene, butyl hydroxyanisole, p-methoxyphenol, cresol,pyrogallol, 3,5-di-t-butyl-4-hydroxytoluene,2,2′-methylenebis(4-methyl-6-t-butylphenol),2,2′-methylenebis(4-ethyl-6-butylphenol), and4,4′-thiobis(3-methyl-6-t-butylphenol); and hindered amines such as acompound having a 2,2,6,6-tetramethylpiperidine-N-oxyl skeleton, acompound having a 2,2,6,6-tetramethylpiperidine skeleton, a compoundhaving a 2,2,6,6-tetramethylpiperidine-N-alkyl skeleton, and a compoundhaving a 2,2,6,6-tetramethylpiperidine-N-acyl skeleton. Moreover, thepolymerization inhibitors may be used alone or two or more kinds may beused in combination.

The content of the polymerization inhibitor is preferably 0.050% by massto 0.50% by mass, more preferably 0.10% by mass to 0.40% by mass, stillmore preferably 0.15% by mass to 0.25% by mass with respect to the totalamount of the maintenance liquid. When the content of the polymerizationinitiator is equal to or greater than 0.050% by mass, cleaning abilityat the time of maintenance tends to be further improved. In addition,when the content of the polymerization initiator is equal to or lessthan 0.50% by mass, reduction in the curability of an ultraviolet raycurable-type composition after maintenance tends to be furthersuppressed.

Solvent

The maintenance liquid of the embodiment may further include a solvent.The solvent is not particularly limited, and for example, an organicsolvent or water can be used.

Examples of the water include water in which ionic impurities areremoved as much as possible such as ultrapure water and pure water suchas ion exchange water, ultrafiltrated water, reverse osmosis water, ordistilled water. In addition, when water sterilized by irradiating withan ultraviolet ray or adding hydrogen peroxide is used, it is possibleto prevent generation of fungi or bacteria in a case where themaintenance liquid is stored for a long period of time. Thus, storagestability tends to be further improved.

Examples of the organic solvent, which are not particularly limited,include alcohols or glycols such as glycerin, ethylene glycol,diethylene glycol, triethylene glycol, propylene glycol, dipropyleneglycol, 1,3-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,4-butanediol, 1,5-pentane diol, 1,6-hexane diol, diethyleneglycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether,diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butylether, ethylene glycol mono-t-butyl ether, diethylene glycolmono-n-butyl ether, triethylene glycol monobutyl ether, diethyleneglycol mono-t-butyl ether, propylene glycol monomethyl ether, propyleneglycol monoethyl ether, propylene glycol mono-t-butyl ether, propyleneglycol mono-n-propyl ether, propylene glycol mono-iso-propyl ether,propylene glycol mono-n-butyl ether, dipropylene glycol mono-n-butylether, dipropylene glycol mono-n-propyl ether, dipropylene glycolmono-iso-propyl ether, tripropylene glycol monomethyl ether, diethyleneglycol dimethyl ether, diethylene glycol diethyl ether, diethyleneglycol dibutyl ether, diethylene glycol ethyl methyl ether, diethyleneglycol butyl methyl ether, triethylene glycol dimethyl ether,tetraethylene glycol dimethyl ether, dipropylene glycol dimethyl ether,dipropylene glycol diethyl ether, tripropylene glycol dimethyl ether,methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, n-butanol,2-butanol, tert-butanol, iso-butanol, n-pentanol, 2-pentanol,3-pentanol, and tert-pentanol; N,N-dimethylformamide,N,N-dimethylacetamide, 2-pyrrolidone, N-methyl-2-pyrrolidone,2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide,sulfolane, and 1,1,3,3-tetramethyl urea. The organic solvents may beused alone or two or more kinds may be used in combination.

Other Components

In the maintenance liquid of the embodiment, various additives such as asolubilizer, a viscosity modifier, a pH adjusting agent, an antioxidant,a preservative, an antifungal agent, a corrosion inhibitor, and achelating agent for capturing metal ions which affect dispersion canalso be suitably added in order to maintain the preservation stabilitythereof and the discharge stability of the head to be excellent, toimprove the clogging, or to prevent deterioration of the maintenanceliquid.

Viscosity

The viscosity of the maintenance liquid at 20° C. is preferably equal toor less than 20 mPa·s, more preferably equal to or less than 17.5 mPa·s,and still more preferably equal to or less than 15 mPa·s. When theviscosity of the maintenance liquid at 20° C. is in the above-describedrange, cleaning ability at the time of maintenance tends to be furtherexcellent. In addition, although the lower limit of the viscosity of themaintenance liquid at 20° C. is not particularly limited, the lowerlimit is preferably equal to or greater than 5.0 mPa·s. The viscositycan be measured by the methods described in Examples.

The viscosity of the maintenance liquid at 20° C. is lower than theviscosity of an ultraviolet ray curable-type composition at 20° C.preferably by equal to or greater than 5.0 mPa·s, more preferably byequal to or greater than 4.0 mPa·s, and still more preferably by equalto or greater than 3.0 mPa·s. When the viscosity of the maintenanceliquid at 20° C. is lower than the viscosity of an ultraviolet raycurable-type composition at 20° C. by equal to or greater than 5.0mPa·s, cleaning ability at the time of maintenance tends to be furtherimproved.

The solubility parameter of the maintenance liquid is preferably equalto or greater than 5.0, more preferably equal to or greater than 7.5,and still more preferably equal to or greater than 10. When thesolubility parameter of the maintenance liquid is equal to or greaterthan 5.0, cleaning ability at the time of maintenance tends to befurther improved. Moreover, although the upper limit of the solubilityparameter of the maintenance liquid is not particularly limited, theupper limit is preferably equal to or less than 20.

In addition, the solubility parameter of the maintenance liquid isgreater than the solubility parameter of an ultraviolet ray curable-typecomposition described below preferably by equal to or greater than 0.50,more preferably by equal to or greater than 1.0, and still morepreferably by equal to or greater than 2.0. When the solubilityparameter of the maintenance liquid is greater than the solubilityparameter of an ultraviolet ray curable-type composition by equal to orgreater than 0.5, cleaning ability at the time of maintenance tends tobe further improved.

Moreover, the solubility parameter (SP value) of a composition(maintenance liquid and ultraviolet ray curable-type composition) can bedetermined by the following equation.

Solubility parameter (SP value)=solubility of acyl phosphine oxide-basedphotopolymerization initiator in polymerizable compound×content (% bymass) with respect to composition (100 parts by mass) of thepolymerizable compound÷100

(In a case where the composition includes plural polymerizablecompounds, the solubility parameter is the sum total obtained by addingthe above values.) Maintenance

The maintenance liquid of the embodiment is used in maintenance of adevice equipped with a discharge head for discharging an ultraviolet raycurable-type composition containing an acyl phosphine oxide-basedphotopolymerization initiator toward an attachment object. Hereinafter,a recording apparatus as an embodiment of the device will be described,and the device may be a device equipped with a discharge head. Here, theterm “maintenance” refers to cleaning a recording apparatus, replacingan ultraviolet ray curable-type composition in a composition flow pathin the recording apparatus with the maintenance liquid, and filling theinside of the composition flow path with the maintenance liquid. Here,the term “composition flow path” refers to a flow path for circulatingan ultraviolet ray curable-type composition in a recording apparatus.Examples of the composition flow path include an ultraviolet raycurable-type composition container for storing the ultraviolet raycurable-type composition, a supply path for supplying the ultravioletray curable-type composition from the ultraviolet ray curable-typecomposition container to a discharge head, and a flow path forcirculating the ultraviolet ray curable-type composition in thedischarge head to a nozzle opening.

A cleaning target member is at least any one of all members to which anultraviolet ray curable-type composition can be attached, such as acomposition flow path, the inside of head, a nozzle plate, a cap, and awiper of a recording apparatus. Examples of the cleaning method, whichare not particularly limited, include a method of circulating amaintenance liquid to the composition flow path of a recording apparatusand a method of attaching a maintenance liquid to a nozzle plate, a cap,and a wiper.

A method of replacing the ultraviolet ray curable-type composition inthe composition flow path of a recording apparatus with the maintenanceliquid, and a method of filling the inside of the composition flow pathwith the maintenance liquid are not particularly limited. For example,in the case of increasing the initial filling ability of the ultravioletray curable-type composition, before filling with the ultraviolet raycurable-type composition, it is preferable to fill the ultraviolet raycurable-type composition container on the upstream side with themaintenance liquid. As a result, it is possible to efficiently removebubbles generated in the ultraviolet ray curable-type compositioncontainer when filling with the ultraviolet ray curable-type compositionand bubbles in the ultraviolet ray curable-type composition flow path,and it is possible to improve the filling ability of the ultraviolet raycurable-type composition.

In addition, in the case where an image is not recorded using therecording apparatus for a long period of time or a discharge failureoccurs, it is possible to replace the ultraviolet ray curable-typecomposition in the composition flow path with the maintenance liquid.The replacement with the maintenance liquid can be performed byreplacing the ultraviolet ray curable-type composition in thecomposition flow path with the maintenance liquid by flowing themaintenance liquid into the composition flow path filled with theultraviolet ray curable-type composition. At this time, before themaintenance liquid is flowed into, the ultraviolet ray curable-typecomposition in the composition flow path may be discharged out of thesystem.

On the other hand, in the case where recording is restarted using therecording apparatus, the maintenance liquid may be replaced with theultraviolet ray curable-type composition by flowing the ultraviolet raycurable-type composition into the composition flow path filled with themaintenance liquid and discharging the maintenance liquid from a nozzleopening. At this time, before the ultraviolet ray curable-typecomposition is flowed into, the maintenance liquid in the compositionflow path may be discharged from the nozzle opening.

In addition, when filling the composition flow path with the ultravioletray curable-type composition or the maintenance liquid, filling may beperformed by changing the ultraviolet ray curable-type composition andthe maintenance liquid by a normal cleaning operation. In addition,filling may be performed by capping a cap having a through hole on thenozzle opening surface of the discharge head, by generating a negativepressure in the cap by a suction pump which communicates with thethrough hole through a tube, and by circulating the ultraviolet raycurable-type composition or the maintenance liquid into the compositionflow path.

In this manner, by using the maintenance liquid, it is possible toprevent a cured product derived from the ultraviolet ray curable-typecomposition from remaining on members to which the ultraviolet raycurable-type composition can be attached, such as a composition flowpath, a nozzle plate, a cap, and a wiper of the recording apparatus.

Recording Apparatus

The recording apparatus is equipped with a discharge head fordischarging the ultraviolet ray curable-type composition containing theacyl phosphine oxide-based photopolymerization initiator toward anattachment object. More specifically, the recording apparatus isequipped with a composition supply system, and performs recording bydischarging the ultraviolet ray curable-type composition supplied fromthe ultraviolet ray curable-type composition container to the dischargehead toward an attachment object from the discharge head. Hereinafter,the recording apparatus of the embodiment will be described in detail.

Discharge Head

The discharge head discharges the ultraviolet ray curable-typecomposition containing the acyl phosphine oxide-basedphotopolymerization initiator toward an attachment object. Due to this,the ultraviolet ray curable-type composition is attached to theattachment object. The discharge head is preferably equipped with aheating mechanism for heating the ultraviolet ray curable-typecomposition. Thus, the viscosity of the ultraviolet ray curable-typecomposition can be reduced, and thus, the recording apparatus has anexcellent discharge stability.

The recording apparatus is preferably equipped with a light sourceirradiating the ultraviolet ray curable-type composition attached to theattachment object with ultraviolet rays (ultraviolet light). Thephotopolymerization initiator included in the ultraviolet raycurable-type composition is decomposed by irradiation with ultravioletrays from a light source, due to this, initiating species such as aradical, an acid, and a base are generated, and the polymerizationreaction of the polymerizable compound is promoted by functions of theinitiating species. Alternatively, the polymerization reaction of thepolymerizable compound included in the ultraviolet ray curable-typecomposition is initiated by irradiation with ultraviolet rays.

As the light source (ultraviolet rays source), a semiconductor lightsource is preferable. Examples of the semiconductor light source includeultraviolet ray emitting elements (light emitting diodes) such as anultraviolet ray emitting diode (UV-LED) and an ultraviolet ray laserdiode (UV-LD). Among these, the recording apparatus is preferablyequipped with an ultraviolet ray emitting element for irradiating thedischarged ultraviolet ray curable-type composition with ultravioletrays. By using the semiconductor light source, miniaturization and along life of the recording apparatus, and a high efficiency of arecording method, reduction in power consumption, reduction in heatgeneration, and reduction in cost are possible compared to a case ofusing a metal halide light source or a mercury lamp. In addition, theemission peak wavelength of the ultraviolet ray emitting diode ispreferably in a range of 360 nm to 420 nm. By using such a peakwavelength, the curability of the ultraviolet ray curable-typecomposition tends to be further improved. The energy of irradiation withrespect to the ultraviolet ray curable-type composition attached to theattachment object is preferably 100 mJ/cm² to 1000 mJ/cm², and morepreferably 200 mJ/cm² to 600 mJ/cm² in terms of performing sufficientcuring.

Composition Supply System

For example, the composition supply system is equipped with anultraviolet ray curable-type composition container, a discharge headhaving a nozzle for discharging the ultraviolet ray curable-typecomposition, and a composition supply path which connects theultraviolet ray curable-type composition container and the dischargehead, and supplies the above-described liquid from the ultraviolet raycurable-type composition container to the discharge head.

The recording apparatus equipped with the composition supply system canbe classified into several types according to a system of the recordingapparatus or a supply system of the ultraviolet ray curable-typecomposition. Examples of the system of the recording apparatus includetwo-dimensional recording apparatuses such as a line printer and aserial printer, and three-dimensional recording apparatuses. The lineprinter is a printer equipped with a line head having a lengthcorresponding to the width of the attachment object, and in the lineprinter, a head is fixed so as (almost) not to be moved, and printing isperformed in one pass (single pass). On the other hand, in the serialprinter, while a head reciprocates (shuttle-moves) in the directionperpendicular to a transportation direction of an attachment object,printing is performed in two or more passes (multi passes). In addition,the three-dimensional recording apparatus forms a three-dimensionalobject by stacking cross-sectional shapes based on the data of ComputerAided Design (CAD). In addition, as the supply system of the ultravioletray curable-type composition, an off-carriage type in which theultraviolet ray curable-type composition container and the dischargehead of a carriage are connected by a composition supply path such as atube or the like can be exemplified.

Attachment Object

The attachment object refers to a two-dimensional recording medium inthe case of the two-dimensional recording apparatus. In addition, in thecase of the three-dimensional recording apparatus of stackingcross-sectional shape patterns by repeating a step in which theultraviolet ray curable-type composition is discharged to a stage, across-sectional shape pattern is manufactured by curing the dischargedultraviolet ray curable-type composition by irradiation with ultravioletrays, the ultraviolet ray curable-type composition is further dischargedto the manufactured cross-sectional shape pattern, and the dischargedultraviolet ray curable-type composition is cured, the attachment objectbecomes a stage or a cured ultraviolet ray curable-type composition.

As the two-dimensional recording apparatus, an absorbing recordingmedium or a non-absorbing recording medium can be exemplified. Examplesof the absorbing recording medium, which are not particularly limited,include plain paper such as electrophotographic paper in whichpenetrability of the ultraviolet ray curable-type composition is high,ink jet paper (paper used exclusively for an ink jet provided with anultraviolet ray curable-type composition absorbing layer composed ofsilica particles or alumina particles, or an ultraviolet raycurable-type composition absorbing layer composed of a hydrophilicpolymer such as polyvinyl alcohol (PVA) or polyvinyl pyrrolidone (PVP)),and art paper, coated paper, and cast paper used in general offsetprinting in which penetrability of the ultraviolet ray curable-typecomposition is relatively low.

In addition, examples of the non-absorbing recording medium, which arenot particularly limited, include films or plates made of plastics suchas polyvinyl chloride, polyethylene, polypropylene, and polyethyleneterephthalate (PET), plates made of metals such as iron, silver, copper,and aluminum, metal plates or films made of plastic produced bydeposition of these various metals, plates made of alloy of stainless orbrass, and the like. Ultraviolet Ray Curable-Type Composition

The ultraviolet ray curable-type composition contains the acyl phosphineoxide-based photopolymerization initiator. In addition, the ultravioletray curable-type composition preferably includes the polymerizablecompound which can be included in the maintenance liquid.

Acyl Phosphine Oxide-Based Photopolymerization Initiator

The acyl phosphine oxide-based photopolymerization initiator is suitablefor curing of the ultraviolet ray curable-type composition using an LEDof long wavelength light. Thus, by using the acyl phosphine oxide-basedphotopolymerization initiator, there is a tendency that a curing processby UV-LED becomes excellent, and the curability and the adhesiveness ofthe ultraviolet ray curable-type composition are further improved. Themaintenance liquid of the embodiment can be used in the recordingapparatus using the ultraviolet ray curable-type composition includingsuch a polymerization initiator. Moreover, in the case of using the acylphosphine oxide-based photopolymerization initiator, there is a problemthat the acyl phosphine oxide-based photopolymerization initiator islikely to precipitate at the time of maintenance, however, in the caseof using the maintenance liquid of the embodiment, it is possible tosuppress such precipitation, and cleaning ability is excellent.

The acyl phosphine oxide-based photopolymerization initiator included inthe ultraviolet ray curable-type composition may be the same as thatused in the measurement of the saturation solubility in Examples withrespect to the polymerizable compound included in the maintenanceliquid, may be other acyl phosphine oxide-based photopolymerizationinitiators, and may include plural types of acyl phosphine oxide-basedphotopolymerization initiators. The tendency of the magnitude ofsolubility with respect to the polymerizable compound of other acylphosphine oxide-based photopolymerization initiators has also the sametendency as that of the acyl phosphine oxide-based photopolymerizationinitiator used in the measurement of the saturation solubility inExamples, and in the present embodiment, by using the polymerizablecompound in which the saturation solubility at 20° C. of the acylphosphine oxide-based photopolymerization initiator used in themeasurement of the saturation solubility in Examples is equal to orgreater than 5.0% by mass in the maintenance liquid, it is possible toexhibit the effect described above in maintenance of a device equippedwith a discharge head for discharging the ultraviolet ray curable-typecomposition containing other various acyl phosphine oxide-basedphotopolymerization initiators. As the acyl phosphine oxide-basedphotopolymerization initiator included in the ultraviolet raycurable-type composition, the acyl phosphine oxide-basedphotopolymerization initiator used in the measurement of the saturationsolubility in Examples is more preferable, or other acyl phosphineoxide-based photopolymerization initiators in which the saturationsolubility in the case of measuring in the same manner as in themeasurement of the saturation solubility in Examples except for usingother acyl phosphine oxide-based photopolymerization initiators becomesgreater than the saturation solubility measured in the measurement ofthe saturation solubility in Examples are also more preferable.

Specific examples of the acyl phosphine oxide-based photopolymerizationinitiator, which are not particularly limited, includebis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide,2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, andbis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide.

Examples of commercially available products of the acyl phosphineoxide-based photopolymerization initiator, which are not particularlylimited, include IRGACURE 819(bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide), DAROCUR TPO(2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), andbis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide.

The content of the acyl phosphine oxide-based photopolymerizationinitiator is preferably equal to or greater than 5.0% by mass, morepreferably equal to or greater than 6.0% by mass, and still morepreferably equal to or greater than 8.0% by mass with respect to thetotal amount of the ultraviolet ray curable-type composition. When thecontent of the acyl phosphine oxide-based photopolymerization initiatoris equal to or greater than 5.0% by mass, the curability of theultraviolet ray curable-type composition tends to be further improved.In addition, the content of the acyl phosphine oxide-basedphotopolymerization initiator is preferably equal to or less than 12% bymass, and more preferably equal to or less than 10% by mass with respectto the total amount of the ultraviolet ray curable-type composition.When the content of the acyl phosphine oxide-based photopolymerizationinitiator is equal to or less than 12% by mass, cleaning ability at thetime of maintenance tends to be further improved.

Polymerizable Compound

As the polymerizable compound, polymerizable compounds exemplified aspolymerizable compounds which can be included in the maintenance liquid,and other polymerizable compounds can be exemplified. By using thepolymerizable compound in the maintenance liquid, the maintenance liquidcan be used as a head filling liquid, it is possible to reduce the headattack properties in the case of being in a state of being filled for along period of time, and it is possible to improve re-replacementproperties at the time of re-replacing with the ultraviolet raycurable-type composition after maintenance.

The total content of the polymerizable compound in the maintenanceliquid is greater than the total amount of the polymerizable compound inthe ultraviolet ray curable-type composition preferably by equal to orgreater than 10% by mass, and more preferably by 15% by mass to 20% bymass. When the content of the polymerizable compound in the maintenanceliquid is greater than the content of the polymerizable compound in theultraviolet ray curable-type composition by equal to or greater than 10%by mass, there is a tendency that cleaning ability at the time ofmaintenance is further improved, and reduction in the curability of theultraviolet ray curable-type composition after maintenance is furthersuppressed.

Other Components

In the ultraviolet ray curable-type composition used in the embodiment,various additives such as a coloring material such as a pigment or adye, a solubilizer, a viscosity modifier, a pH adjusting agent, anantioxidant, a preservative, an antifungal agent, a corrosion inhibitor,and a chelating agent for capturing metal ions which affect dispersioncan be suitably added.

Maintenance Method

The maintenance method of the embodiment has a step of performingmaintenance of a recording apparatus equipped with a discharge head fordischarging the ultraviolet ray curable-type composition containing theacyl phosphine oxide-based photopolymerization initiator toward anattachment object using the maintenance liquid.

As the recording apparatus, the same apparatus as that described abovecan be exemplified. Specific examples of the operation performed in themaintenance step include cleaning of the recording apparatus,replacement of the ultraviolet ray curable-type composition in thecomposition flow path of the recording apparatus with the maintenanceliquid, and filling of the inside of the composition flow path with themaintenance liquid.

EXAMPLES

Hereinafter, the invention will be more specifically described usingExamples and Comparative Examples. The invention is not limited to theseExamples. Material of Maintenance Liquid and Ultraviolet RayCurable-Type Composition

The main materials of a maintenance liquid and an ultraviolet raycurable-type composition used in the following Examples and ComparativeExamples are as follows. Polymerizable Compound

V#192 (phenoxyethyl acrylate, manufactured by Osaka Organic ChemicalIndustry Ltd., saturation solubility of IRGACURE 819 of 10% by mass,saturation solubility of DAROCUR TPO of 20% by mass, viscosity of 8.7mPa·s, molecular weight of 192)

SR508 (dipropylene glycol diacrylate, manufactured by Sartomer Co.,Ltd., saturation solubility of IRGACURE 819 of 4.0% by mass, saturationsolubility of DAROCUR TPO of 8% by mass, viscosity of 10 mPa·s,molecular weight of 242)

VEEA (2-(2-vinyloxyethoxyl)ethyl acrylate, manufactured by NipponShokubai Co., Ltd., saturation solubility of IRGACURE 819 of 6.0% bymass, saturation solubility of DAROCUR TPO of 12% by mass, viscosity of2.5 mPa·s, molecular weight of 186)

DA-141 (2-hydroxy-3-phenoxypropyl acrylate, manufactured by NagaseChemtex Corporation, saturation solubility of IRGACURE 819 of 5.5% bymass, saturation solubility of DAROCUR TPO of 11% by mass, viscosity of150 mPa·s, molecular weight of 222)

IBXA (isobornyl acrylate, manufactured by Toagosei Co., Ltd., saturationsolubility of IRGACURE 819 of 3.8% by mass, saturation solubility ofDAROCUR TPO of 7.6% by mass, viscosity of 7.7 mPa·s, molecular weight of208)

FA-BZA (benzyl acrylate, manufactured by Hitachi Chemical Co. Ltd.,saturation solubility of IRGACURE 819 of 14.2% by mass, saturationsolubility of DAROCUR TPO of 28.4% by mass, viscosity of 5.5 mPa·s,molecular weight of 162)

LA (lauryl acrylate, manufactured by Osaka Organic Chemical IndustryLtd., saturation solubility of IRGACURE 819 of 2.0% by mass, saturationsolubility of DAROCUR TPO of 4% by mass, viscosity of 4.0 mPa·s,molecular weight of 240)

IOAA (isooctyl acrylate, manufactured by Osaka Organic Chemical IndustryLtd., saturation solubility of IRGACURE 819 of 3.0% by mass, saturationsolubility of DAROCUR TPO of 6% by mass, viscosity of 2.0 mPa·s,molecular weight of 184)

A-DPH (dipentaerythritol hexaacrylate, manufactured by Shin-NakamuraChemical Co., Ltd., saturation solubility of IRGACURE 819 of 1% by mass,saturation solubility of DAROCUR TPO of 2% by mass, viscosity of 6600mPa·s, molecular weight of 578) Solvent

TPGmME (tripropylene glycol monomethyl ether) Surfactant

BYK-UV3500 (manufactured by BASF Corp.) Polymerization Inhibitor

MEHQ (p-methoxyphenol, manufactured by Tokyo Chemical Industry Co.,Ltd.)

Photopolymerization Initiator

IRGACURE 819 (manufactured by BASF Corp.)

DAROCUR TPO (manufactured by BASF Corp.)

IRGACURE 184 (manufactured by BASF Corp.)

IRGACURE 369 (manufactured by BASF Corp.)

Coloring Material

Carbon Black

Preparation of Maintenance Liquid and Ultraviolet Ray Curable-TypeComposition

Each material was mixed according to the composition shown in thefollowing Tables 1 and 2, and the mixture was sufficiently stirred,whereby each maintenance liquid and each ultraviolet ray curable-typecomposition were obtained. Moreover, in the following Tables 1 and 2,the unit of numerical values is % by mass, and the total is 100.0% bymass.

Measurement of Saturation Solubility of Acyl Phosphine Oxide-BasedPhotopolymerization Initiator in Polymerizable Compound

A photopolymerization initiator was added to 300 g of a polymerizablecompound at 20° C., then, the mixture was stirred for 3 hours at astirring rotational speed of 300 rpm, and it was checked whether an acylphosphine oxide-based photopolymerization initiator(bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) was dissolved ornot. This operation was repeated, and the maximum amount added of thedissolved acyl phosphine oxide-based photopolymerization initiator waschecked. Moreover, it was visually checked whether the acyl phosphineoxide-based photopolymerization initiator was dissolved or not, and itwas determined whether the acyl phosphine oxide-basedphotopolymerization initiator was dissolved or not by the presence orabsence of the acyl phosphine oxide-based photopolymerization initiatorremaining in a granular form or cloudiness of overall polymerizablecompound. Based on the maximum amount added of the dissolved acylphosphine oxide-based photopolymerization initiator, the saturationsolubility of the acyl phosphine oxide-based photopolymerizationinitiator in the polymerizable compound was calculated by the followingequation.

Saturation solubility of the acyl phosphine oxide-basedphotopolymerization initiator in the polymerizable compound=maximum massof the dissolved acyl phosphine oxide-based photopolymerizationinitiator/(mass of the polymerizable compound+maximum mass of thedissolved acyl phosphine oxide-based photopolymerizationinitiator)×100(%) Cleaning Ability

A 200 mm polypropylene tube having a diameter of 2 mm was filled withthe ultraviolet ray curable-type composition. 20 mL of the maintenanceliquid was flowed into the polypropylene tube filled with theultraviolet ray curable-type composition at a flow velocity of 0.6g/min. The liquid in the tube after 20 mL of the maintenance liquid wasflowed was collected, then, the collected liquid was diluted to be1/100, and the absorbance thereof was measured. On the basis of theobtained absorbance, the cleaning ability was evaluated according to thefollowing evaluation criteria. A lower absorbance means that themaintenance liquid has higher cleaning ability.

Evaluation Criteria

A: Absorbance was less than 0.5.

B: Absorbance was equal to or greater than 0.5 and less than 1.0.

C: Absorbance was equal to or greater than 1.0, and precipitate derivedfrom polymerization initiator was not generated.

D: Absorbance was equal to or greater than 1.0, and precipitate derivedfrom polymerization initiator was generated.

Viscosity

The viscosities of the maintenance liquid and the ultraviolet raycurable-type composition at 20° C. were measured using a viscometer(trade name: MCR-300, manufactured by Physica Co., Ltd.). On the basisof the obtained viscosity, the viscosity was evaluated according to thefollowing evaluation criteria.

Evaluation Criteria

A: Viscosity at 20° C. was equal to or less than 20 mPa·s.

B: Viscosity at 20° C. was greater than 20 mPa·s.

Odor

The odor of the maintenance liquid was snuffed, and the odor wasevaluated according to the following evaluation criteria.

Evaluation Criteria

A: There was no irritating smell

B: There was irritating smell

Curability of Ultraviolet Ray Curable-Type Composition

The test of the curability of the ultraviolet ray curable-typecomposition was performed using a printer (remodeled PX-7500,manufactured by Seiko Epson Corporation). First, a maintenance liquidcartridge was connected to a discharge head with a 200 mm polypropylenetube having a diameter of 2 mm. Next, in a state in which the portionfrom the tube to the discharge head was filled with the maintenanceliquid, the maintenance liquid cartridge was exchanged with anultraviolet ray curable-type composition cartridge, and 20 mL of theultraviolet ray curable-type composition was flowed to the tube at aflow velocity of 0.6 g/min. Then, the ultraviolet ray curable-typecomposition was discharged to a recording medium (trade name: LumirrorS10, manufactured by Toray Industries, Inc.) from the discharge head,and the ultraviolet ray curable-type composition which was attached tothe recording medium was irradiated with ultraviolet rays having anirradiation energy of 200 mJ/cm², whereby a coating film of solidpattern having a thickness of 10 μm was formed. As the ultraviolet raylamps, an LED having an emission peak wavelength of 395 nm was used. Inaddition, the irradiation intensity [mW/cm²] on the irradiated surfaceto be radiated from the light source was measured, and from the productof the irradiation intensity and a duration of irradiation [s], theirradiation energy [mJ/cm²] was determined. The measurement of theirradiation intensity was performed using an ultraviolet ray intensitymeter UM-10 and a light-receiving unit UM-400 (manufactured by KonicaMinolta Sensing, Inc.).

The obtained coating film was rubbed with a cotton swab under theconditions of a load of 100 gN, a case where the ultraviolet raycurable-type composition was attached to the cotton swab or a case wherethe coating film of the ultraviolet ray curable-type composition on arecording medium was scratched was determined to have tackiness. On thebasis of the determination of the tackiness, the curability of theultraviolet ray curable-type composition was evaluated according to thefollowing evaluation criteria.

Evaluation Criteria

A: Tackiness was not confirmed.

B: Curing of a coating film was confirmed, however, scratches of thecoating film were observed, and thus, tackiness was confirmed.

C: Curing defects of a coating film were confirmed, and the coating filmwas in the state in which wet feeling totally remained.

TABLE 1 Example 1 2 3 4 5 6 7 Maintenance Maintenance liquid No. 1 2 3 45 6 7 liquid Polymerizable compound V#192 40 40 19.3 40 40 40 40 SR50819.3 29.3 40 19.3 19.3 19.3 19.3 VEEA 40 30 40 DA-141 40 IBXA 40 FA-BZA40 LA 40 IOOA Solvent TPGmME Surfactant BYK-UV3500 0.5 0.5 0.5 0.5 0.50.5 0.5 Polymerization inhibitor MEHQ 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Total100 100 100 100 100 100 100 Content of polymerizable compound 80 70 59.380 40 80 40 in which saturation solubility is equal to or greater than5% Solubility parameter 7.17 6.97 5.93 6.67 6.29 10.45 5.57 Ultravioletray curable-type composition No. 1 1 1 1 1 1 1 Cleaning ability A A B BB A C Viscosity A A A B A A A Odor A A A A A B A Curability ofultraviolet ray curable-type composition A A A A A A A ExampleComparative Example 8 9 1 2 3 4 5 Maintenance Maintenance liquid No. 8 91 3 10 11 10 liquid Polymerizable compound V#192 40 40 40 19.3 SR50819.3 19.8 19.3 40 19.3 19.3 VEEA 40 40 40 DA-141 IBXA FA-BZA LA 40 40IOOA 40 40 40 Solvent TPGmME 100 Surfactant BYK-UV3500 0.5 0.5 0.5 0.50.5 Polymerization inhibitor MEHQ 0.2 0.2 0.2 0.2 0.2 0.2 Total 100 100100 100 100 100 100 Content of polymerizable compound 40 80 80 59.3 0 00 in which saturation solubility is equal to or greater than 5%Solubility parameter 5.97 7.19 7.17 5.93 2.77 — 2.77 Ultraviolet raycurable-type composition No. 1 1 2 2 1 1 2 Cleaning ability C B A A D AB Viscosity A A A A A A A Odor A A A A A A A Curability of ultravioletray curable-type composition A A B B A C B

TABLE 2 Ultraviolet ray Ultraviolet ray curable-type 1 2 curable-typecomposition No. composition Polymerizable V#192 30 30 compound SR508 3030 VEEA 20 20 A-DPH 8.3 8.3 Photopolymerization IRGACURE 819 5 initiatorDAROCUR TPO 4 IRGACURE 184 4 IRGACURE 369 5 Surfactant BYK-UV3500 0.50.5 Polymerization MEHQ 0.2 0.2 inhibitor Coloring material Carbon black2 2 Total 100 100 Content of polymerizable compound in 50 50 whichsaturation solubility is equal to or greater than 5% Viscosity B B

In Comparative Examples 1 and 2, it was found that in the case of arecording apparatus using an ultraviolet ray curable-type compositioncontaining a polymerization initiator other than the acyl phosphineoxide-based photopolymerization initiator, the curability of theultraviolet ray curable-type composition was poor.

In Comparative Example 3, it was found that cleaning ability was poorsince the maintenance liquid included polymerizable compounds, but apolymerizable compound in which the saturation solubility of the acylphosphine oxide-based photopolymerization initiator at 20° C. was equalto or greater than 5.0% by mass was not included.

In addition, in Comparative Example 4, it was found that the curabilityof the ultraviolet ray curable-type composition after maintenance waspoor since the maintenance liquid did not include any polymerizablecompound.

Furthermore, in Comparative Example 5, it was found that when theultraviolet ray curable-type composition used in a recording apparatusdid not include the acyl phosphine oxide-based photopolymerizationinitiator, cleaning ability was relatively favorable even in the casewhere the maintenance liquid did not include a polymerizable compound inwhich the saturation solubility of the acyl phosphine oxide-basedphotopolymerization initiator at 20° C. was equal to or greater than5.0% by mass, however, the curability of the ultraviolet raycurable-type composition was poor similarly to that in ComparativeExamples 1 and 2. Based on what has been described above, themaintenance liquid of the embodiment is required since excellentcleaning ability is obtained in the case of using an ultraviolet raycurable-type composition having an excellent curability of anultraviolet ray curable-type composition including the acyl phosphineoxide-based photopolymerization initiator.

The entire disclosure of Japanese Patent Application No. 2014-057152,filed Mar. 19, 2014 is expressly incorporated by reference herein.

What is claimed is:
 1. A maintenance liquid which is used in maintenanceof a device equipped with a discharge head for discharging anultraviolet ray curable-type composition containing the acyl phosphineoxide-based photopolymerization initiator toward an attachment objectcomprising: a polymerizable compound in which a saturation solubility ofan acyl phosphine oxide-based photopolymerization initiator at 20° C. isequal to or greater than 5.0% by mass.
 2. The maintenance liquidaccording to claim 1, wherein the polymerizable compound includes atleast any one of vinyl ether group-containing (meth)acrylic acid esterrepresented by the following general formula (1) and a monofunctional(meth)acrylate compound having an aromatic ring.CH₂═CR¹—COOR²—O—CH═CH—R³  (1) (In the formula (1), R¹ represents ahydrogen atom or a methyl group, R² represents a divalent organicresidue having 2 to 20 carbon atoms, and R³ represents a hydrogen atomor a monovalent organic residue having 1 to 11 carbon atoms.)
 3. Themaintenance liquid according to claim 1, wherein the viscosity of thepolymerizable compound at 20° C. is equal to or less than 30 mPa·s. 4.The maintenance liquid according to claim 1, wherein the content of thepolymerizable compound is equal to or greater than 40% by mass withrespect to the total amount of the maintenance liquid.
 5. Themaintenance liquid according to claim 1, wherein the viscosity at 20° C.is equal to or less than 20 mPa·s.
 6. The maintenance liquid accordingto claim 1, wherein the viscosity at 20° C. is lower than the viscosityof the ultraviolet ray curable-type composition at 20° C. by equal to orgreater than 5 mPa·s.
 7. The maintenance liquid according to claim 1,wherein the ultraviolet ray curable-type composition includes thepolymerizable compound, and the content of the polymerizable compound inthe maintenance liquid is larger than the content of the polymerizablecompound in the ultraviolet ray curable-type composition by equal to orgreater than 10% by mass.
 8. The maintenance liquid according to claim1, wherein the saturation solubility of the acyl phosphine oxide-basedphotopolymerization initiator at 20° C. with respect to thepolymerizable compound is equal to or greater than 8.0% by mass.
 9. Themaintenance liquid according to claim 1, further comprising: at leastany one of a silicone-based surfactant and a fluorine-based surfactant.10. The maintenance liquid according to claim 1, wherein the molecularweight of the polymerizable compound is equal to or greater than 170.11. The maintenance liquid according to claim 1, wherein the content ofthe acyl phosphine oxide-based photopolymerization initiator in theultraviolet ray curable-type composition is equal to or greater than5.0% by mass.
 12. The maintenance liquid according to claim 1, wherein asolubility parameter is equal to or greater than 5.0.
 13. Themaintenance liquid according to claim 1, wherein the saturationsolubility is a saturation solubility ofbis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide at 20° C.
 14. Amaintenance method, comprising: performing maintenance of a deviceequipped with a discharge head for discharging an ultraviolet raycurable-type composition containing an acyl phosphine oxide-basedphotopolymerization initiator toward an attachment object using themaintenance liquid according to claim
 1. 15. A maintenance method,comprising: performing maintenance of a device equipped with a dischargehead for discharging an ultraviolet ray curable-type compositioncontaining an acyl phosphine oxide-based photopolymerization initiatortoward an attachment object using the maintenance liquid according toclaim
 2. 16. A maintenance method, comprising: performing maintenance ofa device equipped with a discharge head for discharging an ultravioletray curable-type composition containing an acyl phosphine oxide-basedphotopolymerization initiator toward an attachment object using themaintenance liquid according to claim
 3. 17. A maintenance method,comprising: performing maintenance of a device equipped with a dischargehead for discharging an ultraviolet ray curable-type compositioncontaining an acyl phosphine oxide-based photopolymerization initiatortoward an attachment object using the maintenance liquid according toclaim
 4. 18. A maintenance method, comprising: performing maintenance ofa device equipped with a discharge head for discharging an ultravioletray curable-type composition containing an acyl phosphine oxide-basedphotopolymerization initiator toward an attachment object using themaintenance liquid according to claim
 5. 19. The maintenance methodaccording to claim 14, wherein the device has an ultraviolet rayemitting diode for irradiating the discharged ultraviolet raycurable-type composition with ultraviolet rays, and the ultraviolet rayemitting element has an emission peak wavelength in a range of 360 nm to420 nm.
 20. The maintenance method according to claim 14, wherein thedevice is equipped with a heating mechanism for heating the ultravioletray curable-type composition, and discharges the heated composition.